The present invention relates to an oxide-superconducting coil, and especially, to a wind-and-react type coil using a metal sheathed oxide superconducting wire, and a method for manufacturing the same.
As methods for manufacturing an oxide superconducting wire, a powder-in-tube method, wherein superconducting powder, or a precursor of the superconducting powder, is filled in a metallic sheath, such as a silver tube, and the powder filled sheath is manufactured by a processing such as wire drawing, rolling, and other processes, or a dip-coat method, wherein a substrate is dipped into a suspended liquid containing superconducting powder continuously for coating both planes of the substrate with the suspended liquid, have been conventionally utilized. A superconducting coil using the superconducting wire manufactured by any one of the above methods, and manufactured by a wind-and-react (W & R) method, wherein a heat treatment is performed after fabrication of the coil, or a react-and-wind (R & W) method, wherein a heat treatment is performed prior to fabrication of the coil, has been reported to be able to generate a magnetic field of 3-4 T class under a condition of no backup magnetic field (Ookura et al.: Proceedings of The 53rd. 1995 Annual Meeting (Spring time) of the Cryogenic Engineering and Superconductor Society: D2-2 (1995)), and a magnetic field of 1-2 T under a backup magnetic field exceeding 20 T at 4.2 K (N. Tomita et al.: Appl. Phys. Lett., 65 (7), Aug. 15, 1994, p 898-900).
An oxide superconducting coil had problems such that high performance of the oxide superconducting coil estimated from characteristics of its short sample wire element could not be realized practically, on account of a large electromagnetic force under a strong magnetic field, a creep deformation by its own weight occurring during a heat treatment after fabrication of the coil, a thermal reaction of the superconducting core with an insulating material, and the like.
In detail, there were problems such as (1) breakage of the coil by the effect of an electromagnetic force of 40 MPa when the oxide superconducting coil was installed in an external magnetic field of 20 T and an electric current of 200 A was supplied thereto, (2) thermal creep deformation of the coil due to its own weight when a large scale coil was fabricated using the W & R method, and (3) deterioration of the superconductor in characteristics of the critical current density (Jc) caused by a reaction of the superconductor in the wire material core with a ceramic insulator, which was wound together with the superconductor in the wire material core, during heat treatment.